Enhanced control of a microwave heating system

Abstract

A method for controlling a microwave heating system is provided. The method may be used with a system having a liquid-filled microwave heating chamber and includes measuring the value of one or more microwave system parameters. Suitable parameters can include, for example, net microwave power discharged, the temperature of the liquid in the microwave chamber, the flow rate of liquid through the microwave chamber, and the speed of the conveyance system disposed within the microwave chamber. The measured value of the selected parameter is then compared to a target value for that parameter in order to determine a difference. Based on the difference, one or more actions can be taken in order to start, stop, or alter the operation of the microwave heating system.

The invention claimed is: 
     
       1. A method for controlling a microwave heating system, said method comprising:
 (a) generating microwave energy using one or more microwave generators; 
 (b) passing a plurality of articles through a microwave chamber via a conveyance system, wherein at least 50 percent of the volume of said microwave chamber is filled with an incompressible liquid comprising water, and wherein said articles are at least partially submerged in said incompressible liquid during said passing of said articles through said microwave chamber; 
 (c) directing at least a portion of said microwave energy into said microwave chamber via two or more microwave launchers to thereby heat at least a portion of said articles; 
 (d) during at least a portion of steps (a) through (c), operating said microwave heating system according to a prescribed heating profile suitable for heating said articles, wherein said operating includes determining a value for at least one microwave system parameter to thereby provide a measured parameter value, wherein said determining is performed by measuring said value for said microwave system parameter with an automatic control system, wherein said prescribed heating profile has been obtained prior to step (a) by performing the following steps in a small-scale microwave heating system—
 (i) loading at least one of said articles into a small-scale heating chamber of said small-scale microwave heating system; 
 (ii) heating said articles in said small-scale heating chamber by introducing microwave energy into said small-scale heating chamber; and 
 (iii) determining said prescribed heating profile based on said heating of step (ii), wherein said prescribed heating profile includes a predetermined target value for said microwave system parameter; 
 
 (e) comparing said measured parameter value measured during said operating of step (d) with said predetermined target value for said microwave system parameter in said prescribed heating profile to determine a difference, wherein said comparing is performed by said automatic control system; and 
 (f) when said difference determined by said automatic control system in step (e) exceeds a predetermined maximum difference, taking an action with regard to said microwave heating system, 
 wherein said microwave system parameter is selected from the group consisting of net microwave power, temperature of said incompressible liquid in said microwave chamber, flow rate of said incompressible liquid through said microwave chamber, and conveyance system speed, and 
 wherein said action taken in step (f) is selected from the group consisting of stopping said conveyance system, turning off one or more of said generators, increasing or decreasing the output of one or more of said generators, and removing or isolating or re-running or disposing of at least a portion of said articles that were passing through said microwave chamber when said difference determined in step (e) exceeded said predetermined maximum difference. 
 
     
     
       2. A method of controlling a microwave heating system, said method comprising:
 (a) generating microwave energy with at least one microwave generator; 
 (b) passing at least a portion of said microwave energy through a first waveguide segment; 
 (c) discharging at least a portion of said microwave energy from said first waveguide segment into a microwave chamber via at least one microwave launcher to thereby heat a plurality of articles passing through said microwave chamber along a convey line, wherein at least 50 percent of the volume of said microwave chamber is filled with an incompressible liquid comprising water, wherein said articles are at least partially submerged in said incompressible liquid during said discharging of said microwave energy; 
 (d) determining a first value for net power discharged from said microwave launcher using a first pair of directional couplers; 
 (e) determining a second value for net power discharged from said microwave launcher using a second pair of directional couplers, wherein said determining of step (d) performed using said first pair of directional couplers and said determining of step (e) performed using said second pair of directional couplers are carried out independently from one another; 
 (f) comparing at least one of said first value for net power discharged and said second value for net power discharged with a predetermined target value, wherein said comparing is performed using an automatic control system; and 
 (g) taking an action with regard to said microwave heating system when at least one of the following circumstances (i) through (iii) occurs—
 (i) said predetermined target value is a maximum difference between said first value for net power discharged and said second value for net power discharged, and the difference between said first value for net power discharged determined in step (d) and said second value for net power discharged determined in step (e) exceeds said predetermined target value; 
 (ii) said predetermined target value is a minimum value for net power discharged and at least one of said first value for net power discharged determined in step (d) and said second value for net power discharged determined in step (e) falls below said predetermined target value; and 
 (iii) said predetermined target value is a maximum for net power discharged and at least one of said first value for net power discharged determined in step (d) and said second value for net power discharged determined in step (e) exceeds said predetermined target value, and 
 
 wherein said action taken in step (g) is selected from the group consisting of shutting down said generator, stopping said convey line, increasing or decreasing the amount of microwave energy generated by said generator, and removing or isolating or disposing of or re-running one or more of said articles that were passing through the microwave chamber when at least one of circumstances (i) through (iii) occurred. 
 
     
     
       3. The method of  claim 1 , wherein step (f) is carried out when said predetermined maximum difference is at least 5 percent of said predetermined target value. 
     
     
       4. The method of  claim 1 , wherein said operating of step (d) includes determining a value for said temperature of said incompressible liquid in said microwave chamber, wherein said predetermined target value for said temperature of said incompressible liquid in said microwave chamber used during said comparing of step (e) is not more than 130° C. 
     
     
       5. The method of  claim 1 , wherein said operating of step (d) includes determining a value for said flow rate of said incompressible liquid through said microwave chamber, wherein said predetermined target value for said flow rate of said incompressible liquid through said microwave chamber used during said comparing of step (e) is at least 15 gallons per minute (gpm). 
     
     
       6. The method of  claim 1 , wherein said operating of step (d) includes determining a value for said net microwave power, wherein said predetermined target value for said net microwave power used during said comparing of step (e) is at least 75 kW. 
     
     
       7. The method of  claim 6 , wherein said net microwave power is measured using a pair of directional couplers disposed within a waveguide upstream of said at least one of said microwave launchers. 
     
     
       8. The method of  claim 1 , wherein said operating of step (d) includes determining a value for said conveyance system speed, wherein said predetermined target value for said conveyance system speed used during said comparing of step (e) is not more than 10 feet per second (fps). 
     
     
       9. The method of  claim 1 , wherein said operating of step (d) includes determining a value for said temperature of said incompressible liquid in said microwave chamber, wherein said predetermined target value for said temperature of said incompressible liquid in said microwave chamber used during said comparing of step (e) is a minimum temperature of at least 120° C. 
     
     
       10. The method of  claim 1 , wherein said operating of step (d) includes determining a value for said flow rate of incompressible liquid through said microwave chamber, wherein said predetermined target value for said flow rate of incompressible liquid through said microwave chamber used during said comparing of step (e) is a minimum flow rate of at least 5 gpm. 
     
     
       11. The method of  claim 1 , wherein said operating of step (d) includes determining a value for said net microwave power, wherein said predetermined target value used during said comparing of step (e) is a minimum net microwave power of at least 50 kW. 
     
     
       12. The method of  claim 1 , wherein said operating of step (d) includes determining a value for said conveyance system speed, wherein said predetermined target value for said conveyance system speed used during said comparing of step (e) is a maximum speed of not more than 15 fps. 
     
     
       13. The method of  claim 1 , further comprising, prior to step (b), passing said articles through a thermalization zone to thereby thermalize said articles to a substantially uniform outlet temperature such that at least 85 percent of said articles withdrawn from said thermalization zone have a temperature within 5° C. of one another. 
     
     
       14. The method of  claim 1 , wherein said articles comprise packages containing foodstuffs, medical fluids, or medical instruments. 
     
     
       15. The method of  claim 1 , wherein said microwave chamber is pressurized to at least 10 psig and wherein said articles are heated to a temperature where said articles are pasteurized or sterilized. 
     
     
       16. The method of  claim 15 , wherein said articles comprise packaged foodstuffs, wherein said microwave chamber is pressurized to at least 15 psig, and wherein said microwave heating system has a production rate of at least 20 packages per minute per convey line. 
     
     
       17. The method of  claim 2 , wherein said determining of steps (d) and (e) respectively comprise using one of said directional couplers of said first pair and one of said directional couplers of said second pair to measure respective values for forward power, and using the other of said directional couplers of said first pair and the other of said directional couplers of said second pair to measure respective values for reflected power, wherein the differences between said values for forward and reflected power determined for each of said first and said second pairs of directional couplers are said first and said second values for net power discharged, respectively. 
     
     
       18. The method of  claim 2 , wherein said passing of step (b) includes dividing at least a portion of said microwave energy generated in step (a) into two separate portions with a microwave splitter, wherein said discharging of step (c) comprises respectively discharging each of said two separate portions of microwave energy into said microwave chamber via a pair of microwave launchers positioned on opposite sides of said microwave chamber. 
     
     
       19. The method of  claim 18 , wherein said first and said second pair of directional couplers is disposes between said splitter and one of said launchers of said pair of launchers. 
     
     
       20. The method of  claim 2 , wherein said microwave chamber is a pressurized microwave chamber and the heating performed in said chamber pasteurizes or sterilizes said articles. 
     
     
       21. The method of  claim 20 , wherein said articles are selected from the group consisting of foodstuffs, packaged medical fluids, and medical instruments. 
     
     
       22. The method of  claim 21 , wherein said articles comprise packaged foodstuffs, wherein said microwave chamber is pressurized to at least 15 psig, and wherein said microwave heating system has a production rate of at least 20 packages per minute per convey line. 
     
     
       23. The method of  claim 2 , wherein circumstance (i) occurs and said action taken in step (g) is selected from the group consisting of shutting down said generator, increasing or decreasing the amount of microwave energy generated by said generator, and removing or isolating or disposing of one or more of said articles that were passing through the microwave chamber when (i) occurred. 
     
     
       24. The method of  claim 2 , wherein circumstance (ii) occurs and said action taken in step (g) is selected from the group consisting of shutting down said generator, increasing or decreasing the amount of microwave energy generated by said generator, and removing or isolating or disposing of one or more of said articles that were passing through the microwave chamber when (ii) occurred. 
     
     
       25. The method of  claim 2 , wherein circumstance (iii) occurs and said action taken in step (g) is selected from the group consisting of shutting down said generator, increasing or decreasing the amount of microwave energy generated by said generator, and removing or isolating or disposing of one or more of said articles that were passing through the microwave chamber when (iii) occurred.